The present invention is directed to an output and/or input coupler for optical fibers such as light conducting glass fibers.
In optical communication systems, it is often necessary to branch a specific light component out of a main line, for example a bus line, or to feed a light signal into the main line or bus line. This requires input and/or output couplers in which a waveguide overlaps a portion of two waveguides whose end faces are disposed adjacent each other. An example of such an input/output coupler is described in United States patent application Ser. No. 804,398 filed June 7, 1977, which was issued as U.S. Pat. No. 4,164,364 and was based on German patent application No. 26 25 855. In the coupler device described in this application, the device had a planar structure in which two fibers were laterally offset relative to one another. The optical connection between the main fiber and the branching fiber, which enable light to be fed into the main fiber or branched out of the main fiber, was formed by a strip waveguide which was of a light sensitive foil member or a portion of a light sensitive layer. However, at the present time, light guide structures, which utilize light sensitive materials such as light sensitive foils exhibit some undesirable properties which include a relatively high absorption, a deficient resolution and excitation of radiation modes. All of these properties of the light sensitive foil cause attenuation losses. Therefore, such an input and/or output coupler, which utilizes a strip waveguide as part of the coupler has a relatively high insertion loss.